1. Field of the Invention
The field of the present invention relates generally to coaxial transmission lines, and more particularly to support structures for such transmission lines.
2. Discussion of the Relevant Art
The need for a support structure for coaxial transmission lines has been recognized previously in the art. Generally, the presently known support mechanisms will introduce discontinuities or changes in the characteristic impedance of the transmission line. Further, it is commonly known that a transmission line may incorporate a probe for measuring the incident voltage with the reflected signal. To assure proper function this device must be provided with a well defined characteristic impedance, and support means for centrally locating the inner conductor of the coaxial line.
In Banning, U.S. Pat. No. 4,019,162, a coaxial transmission line for ultra high frequency (u.h.f.) waves is shown for use with slotted line equipment, in which transmission line the center conductor is supported coaxially within the surrounding outer conductor by spaced apart dielectric pins extending radially between the conductors, wherein wave reflections are minimized through the application of shallow depressions in the outer surface of the inner conductor about the pins, with the depressions completely surrounding the point of engagement of each pin with the inner conductor, and the depressions being dimensioned to produce an inductive effect for compensating the capacitive effect of the dielectric pins. Banning also discusses the use of holes drilled in the inner conductor, or of circumferential grooves spaced longitudinally ahead of and/or behind the pins being used for providing a support mechanism. Also, the use of beads instead of dielectric pins is discussed, but no teaching is made as to how such beads might be incorporated for providing a support means. The present inventor recognizes that the use of dielectric pins for supporting an inner conductor within an outer conductor of a coaxial transmission line tends to limit the size of the transmission line. Reducing the size of the transmission line while providing for easy assembly tends to preclude the use of such pins. Also, the pins are oftentimes glass reinforced, and as a result tend to become extremely brittle, further complicating the assembly and size reduction problems.
Another Banning patent, U.S. Pat. No. 4,431,255, discloses a coaxial connector having a first dielectric member located in the annular space between the center conductor and outer shell, and a second dielectric member press fit into the shell to surround but not contact the center conductor in the mating region, whereby the second dielectric member provides support to the center conductor during mating of the connector, for providing a desired impedance for use of the connector with coaxial transmission lines at frequencies beyond 26.5 GHz. A simpler method of coupling and supporting the ends of a coaxial transmission line is disclosed in Dench, U.S. Pat. No. 2,922,127, wherein a seal for a coaxial line is taught that includes a ceramic cup for receiving an inner or centrally located conductor of the transmission line and sealing off the same for providing vacuum sealing between the coaxial line and a wave guide.
Ziegler, U.S. Pat. No. 3,437,960, discloses dowel-like dielectric beads for use in high-frequency coaxial connectors, whereby one dielectric bead structure (104) is shown for supporting and sealing the inner conductor of a coaxial line centrally within the outer conductor of the coaxial line near the ends of the line. Ziegler further teaches the use of a spiral bead in a helix-like manner about the length of the inner conductor for providing support for maintaining the inner conductor centrally located within the outer conductor. Another Ziegler patent, U.S. Pat. No. 3,323,083, teaches the use of dowel-like dielectric beads in a coaxial transmission line connector for maintaining an inner conductor centrally located within an outer conductor, whereby the dielectric bead is dimensioned for obtaining a desired impedance.
Bondon, U.S. Pat. No. 3,055,967, shows the use in a coaxial cable of notched insulating tubes arranged in a tightly packed array between the inner and outer conductors of the coaxial cable for maintaining the central positioning of the inner or center conductor. The elongated tubes may be circular or somewhat triangular in shape, and are shown to include radially oriented notches for improving the impedance and loss characteristics of the coaxial cable.
Wheeler, U.S. Pat. No. 2,403,252, teaches the use in a high-frequency matching device of an insulating disk for supporting one end of a centrally located conductor within an outer conductor via use of a pin centrally located in the disk and protruding into the centermost portion of the inner conductor.
The various known arrangements for providing a coaxial transmission line and coaxial transmission line connectors do not permit easy fabrication of relatively small slotted coaxial transmission lines. The use of glass reinforced pins for providing support and spacing means between the inner and outer conductors of a coaxial transmission line tend to cause increasingly difficult assembly problems as the coaxial transmission size is reduced, and are subject to pin breakage because of the brittleness of the material generally used. Also, known techniques of terminating a coaxial transmission line, and for providing coaxial transmission line connectors cause relatively complicated assembly problems, and are difficult to miniaturize.
An object of the present invention is to provide a support structure for a coaxial transmission line that permits easy assembly and size reduction of the line.
Another object of the invention is to provide an improved connector for mating to a coaxial transmission line of reduced size.